On the Planar Geometric Patterns of the Exoskeletal Relief Formation in Early Vertebrates (Osteostraci, Agnatha).

A study of the diversity of sculpture and histological structure of the exoskeleton in various osteostracan taxa (Osteostraci, Agnatha) enabled the first characterization of the main elements (geometric modules) of the planar organization of the complex relief on their armor surface. The armor relief was analyzed using a circular model of the formation of exoskeletal hard structures. The model was applied to unique material, fragments of a shield of the osteostracan Oeselaspis pustulata (Patten, 1931) from the Silurian of the Severnaya Zemlya Archipelago (Russia).

The Vertebrate Exoskeleton: Geometric Patterns of the Armor Relief Formation in Early Jawless Vertebrates (Agnatha, Vertebrata).

Analysis of data on the hard cover structure in various osteostracan taxa (Osteostraci, Agnatha) allowed us to describe geometric patterns of the armor relief formation during morphogenesis of the Vertebrate external skeleton. A circular model of the formation of exoskeletal surface relief has been proposed. A mechanism providing a complete set of the exoskeleton sculpture types was shown to exist already since early Vertebrates.

On the Modes of the Formation of the Exoskeleton in Early Jawless Vertebrates (Osteostraci, Agnatha).

Based on recently obtained original and published data on the fine structure of the external skeleton of osteostracan agnathans (Osteostraci, Agnatha), possible modes of the formation of their hard cover in the course of the horizontal growth of the exoskeleton are characterized. The developmental models for the formation of various configurations of cephalothoracic shields typical for osteostracans are revealed. It is shown that, in the morphogenesis of the hard cover of this group of early vertebrates, a significant part of the variants of the exoskeleton horizontal growth characteristic of early vertebrates are observed.

On the growth and regeneration of the exoskeleton in early jawless vertebrates (Osteostraci, Agnatha).

Based on the study of sculpture of the cephalic shield and histological structure of the exoskeleton in Reticulaspis menneri Afanassieva et Karatajute -Talimaa (Osteostraci, Agnatha) from the Lower Devonian of the Severnaya Zemlya Archipelago, it has been established that, in the ontogeny of the form under study, dentin generation of the exoskeleton may have developed repeatedly, depending on the requirements of the organism. It is established for the first time that, on the shield surface of osteostracans, dentin structures of various types (tubercles, ridges, networks) could be formed both primarily and in subsequent generations with the growth of the exoskeleton. Injury of the integument and, hence, changes in mechanical tension in covering tissues caused activation of the formation of subsequent generations (of dentin) in the areas involved in reparative regeneration of the shield.